This program involves the synthesis and evaluation of transannular peroxides as sensitizers for radiation therapy. These peroxides are capable of releasing oxygen when exposed to x-irradiation. Thus, if such materials can be incorporated into anoxic tumor cells in patients prior to radiation treatment, it may be possible to circumvent the well- known tendency of such cells to survive radiation exposure. 9, 10 - Di (p-carboxyphenyl), 9, 10 - anthracene endoperoxide has been shown to sensitize E. coli. bacteria to radiation damage under both normally oxygenated and anoxic conditions. Sensitization under normal oxygen concentrations is due to formation of a relatively short-lived radiation product of the peroxide. While under anoxic conditions enhancement is apparently due to formation of oxygen either in the normal triplet state, or in an electronically excited singlet state. This peroxide has been shown to also be a radiation sensitizer for a mouse mammary carcinoma (TA-3) treated in vitro under normal oxygenation. It is presently being tested under anoxia. A second transannular peroxide, the 1, 4 - dimethoxy derivative of the above compound has been synthesized and is being tested as a radiation sensitizer as described above.